1. Field of the Disclosure
The present disclosure is related to performing an operation in a wellbore and, in particular, to operation of a laser at a downhole location.
2. Description of the Related Art
In various drilling operations, it is useful to dispose a laser at a downhole location in order to perform a measurement or a downhole operation. Often, the accuracy of a laser-based downhole measurement is dependent on the wavelength of the laser. However, the wavelength of the laser may drift with temperature and/or other downhole conditions. In order to maintain a laser operating at a selected frequency at a downhole location, it is necessary to lock the laser at a selected wavelength. One method of locking a laser includes the use of a Fabry-Perot etalon. The etalon needs to have a low coefficient of expansion and be transparent at laser wavelengths. Zerodur® is a material that meets these requirements but has bad temperature stability at downhole temperatures. However, in a downhole environment, the temperature can range between about 120° C. and 200° C. and the temperature of the Zerodur® needs to be controlled within a few millidegrees in order to achieve high locking precision. Additionally, downhole operations require that this etalon control be maintained for up to 12 hours or longer. Another method of laser locking uses a spectral line of a gas to provide a wavelength standard. This method can also be affected by downhole temperatures and other conditions encountered downhole. Therefore, there is a need to provide a method and apparatus for maintain operation of a laser downhole at a selected wavelength.